Mk6 Transit 125 fuel pressure codes

[tshort1984]

There is no lift pump is there? Its a TDci

[nigel green]

suction pump is built into pump unit

[winterheating]

try testing lift pump by removing fuel temp sensor and testing for pressure at the m12 thread there, you should have around 1 bar at cranking speed, probaly 2 bar at idling speed and up to 6 bar high speed.

Thats handy to know, so that part that the fuel temp sensor is must be after the vacumn transfer part, and before the high pressure chamber in pump.

[winterheating]

You can easily do a high pressure test on the pump anyway......
But with air it would be stupid to look for other faults especially low pressure faults

Was there new ci2 codes generated for the individual injectors then

[winterheating]

if there was indeed air from the filter to pump and return pump to filter, then yes that flow could just be the air circulating, but once the fuel temp gets high enough, it should bypass straight to the tank, and not pull any air back down the flow.
So have you had the return from pump bypassing the filter housing back to tank?? or just the flow bypassing the filter (not such a good idea with this fuel system) to the pump.
Also when a pump is worn fuel temp can get pretty high.

[tshort1984]

yes, new codes were generated.

I cant test the pump here, it will have to be done at the specialists.

winterheating - ironically, the fault occurs more when the engine is hotter. from cold, its fine until engine temp reaches normal operating.

We have tried just a simple bypass of the return direct to tank. There was still air in this system, but no air into the pump. (only under load)

We are under the assumption that the air is getting in somewhere between the inlet on the pump, and the HP chamber. maybe leaking past a seal. This only occurs when maximum demand is required from the engine, as in when the pump is sucking hard, its sucking in air and fuel.

After all, if the pump has got over 250k on it, its about due for a replacement.

Its due to be changed today, so i will let you know.

cheers

[winterheating]

Suppose so, but when they are looked after they can do many many more miles. And if its not the pump itself thats pulling the air in then you will still have to find the fault..............

The vac transfer pump in the FIP can fail a seal and pull in engine oil as the transfer pump is just behind the sprocket.
Suppose if it can fail there it could fail and suck air out side of engine?????

But the more the pump runs the bigger the venturi tee will suck, so could easily be pulling in air from a few joints on that, its only held in pump by 1 or 2 torx screws. Also when fuel is hot and then recirculates straight back to tank the negative pressure maybe more causing more air to be sucked than when fuel is cold.

[tshort1984]

Never managed to get the van in on friday.

What is this "venturi"?

Where is it on the pump, and how much is a new one?

[winterheating]

The plastic part that the return pipe and leak back pipe joins onto.

[nigel green]

FYI

Its not just a bit of plastic!!


The purpose of the venturi is to create a vacuum in the injector return circuit to avoid injector control chamber pressure fluctuations as far as possible. This has the end purpose of avoiding any injection control disturbance.Whilst the venturi is commonly placed on the pump, it can also be placed independently of the pump.

OPERATION The Venturi principle is where a reduction in fuel pressure is induced at points where the speed of fuel flow is increased. Passing through the narrow part the fuel speed of flow increases at the expense of pressure. The internal architecture of the venturi defines its prevailing pressures and flows in the venturi. In the case of the common rail low pressure circuit, the pressure at venturi entry is greater than atmospheric pressure(Pe), the suction value at the discharge return point (Pi) results in a Pe-Pi>O vacuum.